1. Field of the Invention
The present invention relates to an internal combustion engine having a variable flow rate oil pump apparatus, and to a motorcycle including the same. More particularly, the present invention relates to an internal combustion engine having a variable flow rate oil pump apparatus in which an oil passage switching valve arranged in discharge ports of the oil pump apparatus, and a drive shaft of the oil pump apparatus are arranged parallel to a crankshaft of the engine, and to a motorcycle incorporating the same.
2. Description of the Background Art
There is a known variable flow rate oil pump apparatus which has a pump rotor operatively interlocking with a crankshaft of an engine for concurrent rotation therewith, and the known apparatus has a rod-shaped oil passage switching valve arranged in a discharge port of the pump. In the known variable flow rate oil pump apparatus, a hydraulic pressure return opening that faces the discharge port is effectively opened and closed by the operation of the oil passage switching valve, and accordingly, the discharge amount of the entire pump unit can be controlled.
An example of such engine with variable flow rate oil pump apparatus is disclosed in Japanese Unexamined Patent Publication No. 2005-140022.
In the conventional configuration, such as discussed in Japanese Unexamined Patent Publication No. 2005-140022, an axial direction of the oil passage switching valve is arranged so as to be perpendicular to an axial direction of the rotor drive shaft, and thus, also perpendicular to the axial direction of the crankshaft of the engine.
However, when this configuration is applied to an engine for a small vehicle, such as a motorcycle, there is a problem that parts around the pump are likely to be restricted, due to the fact that the space is needed for disposing the oil passage switching valve in the direction which is perpendicular to the axial direction of a rotor drive shaft. With such known configuration, the oil pump, and the engine which contains the oil pump, are likely to become larger.
The present invention has been made to overcome the drawbacks of the known configuration of an engine with a variable flow rate oil pump apparatus. Accordingly, it is one of the objects of the present invention is to reduce the effect on parts around the pump, and simultaneously, to downsize the oil pump, and also to minimize size of the engine having a variable flow rate oil pump apparatus with a rod-shaped oil passage switching valve.